Monkeys have been used extensively as models for the human fetus and infant due to similarities in pre- and postnatal development. The purpose of this study was to determine the potential toxic effects in infant rhesus of an anti-asthmatic compound proposed for use in human pediatric patients. The compound was orally administered beginning on the 4th week of age following a pre-study physical, opthalmologic, and radiographic examination, and complete blood count (CBC) and clinical chemistry screen. Physical signs, food consumption, and body weights were monitored daily, and a physical examination performed at 4, 8, and 12 weeks post-dosing. In addition, the following were assessed during the conduct of the study radiographs and ophthalmologic evaluations (6, 12 wks post-dosing); cbcs, clinical chemistries, urinalyses (4, 8, 12 wks post-dosing), and plasma concentrations of the test compound (day 1 of dosing 2, 4, 8, and 24 hrs post-dosing, and wk 13 post-dosing 1, 2, 4, 6, 8, 24 hrs post-dosing). At roughly 18 wks of age infants were euthanized and a complete necropsy performed. Results of these studies indicated no significant treatment-related findings as evidenced by physical signs, body weight changes, physical examinations, radiographic or ophthalmologic evaluations, hematology, clinical chemistries, or urinalyses. Similarly, no significant gross abnormalities were noted at necropsy at roughly 18 weeks of age.